Patent GB-820766-A (GB)
Title: Improvements in and relating to ophthalmological instruments
IPC: A61B3/028
Filed: 1957-08-15
Abstract: 820,766. Sight-testing apparatus. ABBEY, A. (Amercian Optical Ca ). Aug. 15, 1957, No. 25822/57. Class 97(1) The sight-testing apparatus comprises  a  pair of test units each including a housing with a sight opening for alignment with. a respective eye of a patient and rotatable test element carriers, at least two of which are within the housing, a pair of slides on each of which a test unit is pivoted about an axis normal to and intersecting its sight opening, a transverse track for said slides, mechanism associated with the slides for varying their separation and thus the pupillary distance between the sight openings of the test units, and mechanism for varying the angular relation of the test units relative to the slides and at the same time varying the pupillary distance between the sight openings to adapt the apparatus for "near" testing. In the form shown in Fig. 1, the test units 72, 73, are pivoted, about vertical axes normal to the axes of sight openings 80, to slides 62, 63 movable in a transverse track in a bracket 24 held by a member 20 on a stand. Bracket 24 is pivotal in member 20 but can be clamped thereto by rotating a knob 28 to effect engagement between a tapered flange of member 20 with a projecting collar on bracket 24. The track in bracket 24 is tiltable about a first pin 35 unless screw clamped by a screw press 41 having arms 44, 45. In this track the slides 62 ,63 may move on ball races, each slide having a boss 70, Fig. 5, to which one test unit 72 or 73 is pivoted. Secured to each slide is a nut retainer 84a or 84b which prevents rotation of a nut 87a or 88a on a spindle having right and left-handed threads 87, 88 and operating knobs 89. In this way, rotation of a knob 89 moves the nuts 87a, 88a in opposite directions to vary the separation of the slides and thus the pupillary distance between sight openings 80. In order to set the apparatus for "near" testing, a slot 99 (Fig. 7) is provided in each nut 87a, 88a and is engaged by a pin 94 eccentrically mounted on a member 90 rotatable in the associated slide and having another eccentric pin 95 passing through a port 103 projecting from the test unit and connected to a lever 97. This lever may occupy two detent-defined positions and, by moving it from one position to the other, eccentric 95 pivots the test unit and eccentric 94 alters the separation of the two slides. Stops on each testing unit are adapted to interengage when the pupillary distance is lowered below a certain amount. The two testing units 72, 73 are similar, and as shown for unit 72 in Fig. 11, each includes a housing 77 containing relatively rotatable discs 75, 117 and 118 of which discs 75 and 117 carry "weak" and "strong" spherical lenses respectively and disc 118 carries auxiliary devices. Independent rotation of disc 75 through indexed positions is effected by engaging the knurled edge thereof to bring a required lens into the sight opening 80. If this disc is rotated through more than 360 degrees, a projection thereon activates a Geneva wheel 131 mounted on a slipping clutch 133 so that a gear 141 is driven; this gear has several projecting pins, one of which enters a cut out in the rim of' disc 117 and so rotates its one stop. Lens power indications are given by markings on disc 75 and on a dial 128 carried by disc 117 and having openings through which the markings on disc 75 are visible. The operative markings on both the dial and disc are visible through an opening 127 in housing 77, this opening being closed by a transparent member having a magnifying part. Direct actuation of disc 117 is possible by rotating spindle 137 on which gear 141 is mounted, tne disc 75 in this case remaining stationary. Each test unit is also provided with a rotatable battery of prismatic test elements 82, Fig. 1, each element consisting of two prisms mounted in superposed cells which are rotatable together or through a common control in opposite directions. The upper cell has attached thereto a ring having an index, this ring also having a shoulder carrying a circular scale connected to the lower cell so that the scale and index can be moved in opposite directions. Discs carrying cylindrical lenses may also be provided. An adjustable forehead rest may be pivoted to the bracket 24.